1. Field of the Invention
The present invention relates to an antenna unit for a portable radiotelephone (terminal) in a mobile communications system and, in particular, to an antenna unit having a conductive tube disposed in a main body of the portable radiotelephone.
2. Description of the Related Art
In general, portable radiotelephones, i.e., mobile communications terminals, which are alternatively referred to as xe2x80x9cmobile stationsxe2x80x9d, serve to communicate with one or more xe2x80x9cbase stationsxe2x80x9d by radio to provide their end-users with desired radio telecommunications services. Therefore, by means of these mobile terminals, the subscribed users can be served with a diversity of radio telecommunications services such as telephone calling, e-mail transferring, or internet chatting, etc. Usually, such a mobile communications terminal is provided with at least one antenna unit for receiving and transmitting radio signals in its main body. Recently, a retractable/extendable type of antenna unit has been in wider use to ensure better sensitivity of reception for radio signals.
One of known antenna devices for the mobile communications terminals is illustrated in FIGS. 1 and 2, and consists of a conventional helical antenna and a whip antenna adapted to be retractable into or extendable from an antenna housing. FIG. 1 illustrates the mobile terminal with such a whip antenna 14 (seen extended in FIG. 2) fully retracted into the antenna housing 12, while FIG. 2 illustrates the mobile terminal with the whip antenna 14 fully extended from the antenna housing 12. Accordingly, in case the sensitivity of reception in the antenna goes down, a user may have the whip antenna 14 fully extended out of the antenna housing 12 when using of the mobile terminal. The helical antenna (not shown) is generally positioned within the antenna housing 12 in its longitudinal direction, and when the whip antenna is in a fully retracted position, a rod antenna section 14c is received by an insulating tube 16 disposed in the main body 10. The rod antenna section 14c is provided with an insulator 14b for electrical isolation from the helical antenna and also provided with an antenna cap 14a in its uppermost end. The above figures respectively illustrate the main body 10 of a mobile terminal with its battery pack for power supply removed, wherein reference numeral 10a indicates a bottom surface of the main body.
Referring to FIGS. 3 and 4, the structure and performance of a known antenna unit consisting of a helical antenna (not shown), disposed within an antenna housing 12, and a whip antenna 14 will be described hereinafter. When the whip antenna 14 is in a fully retracted position into the antenna housing, the helical antenna functions as a main antenna. When the whip antenna 14 is in a fully extended position out of the antenna housing, the whip antenna functions as a main antenna. The antenna housing 12 is provided in its lower end with a metal coupling 12a, which is preferably formed in one body with the antenna housing 12 and then screwed to the main body for attachment thereto. To the coupling 12a is coupled the rod antenna section 14c, a lower end of which is further coupled to a stopper 14d, forming an electrical feeder.
The rod antenna section 14c is received by the insulating tube 16 in a retracted position of the whip antenna 14, while the rod antenna section is separated from the insulating tube in an extended position of the whip antenna. This insulating tube is generally disposed in a longitudinal direction adjacent to a bottom surface 10a of the main body, so that it could ensure smooth movement of the whip antenna 14 there through or exclude any physical intervention by any other neighboring elements.
Such a prior art antenna unit usually has a length C1 of an insulator 14b much longer than a length C3 of a helical antenna, in order to ensure that the insulator 14b can keep better isolation between the helical antenna and the whip antenna.
When the whip antenna 14 is in a fully retracted position in the antenna housing 12, any insufficient or incomplete isolation between the whip antenna and the helical antenna is apt to cause the helical antenna to provide low radiation efficiency due to absorption of its radiation energy by the whip antenna. Further, it would also cause a considerable degradation of the reception efficiency for radio signals due to a reduction in a signal-to-noise ratio at a receiver, since the receiver circuit is often affected by noises induced by any harmonic components of digital clocks generated within a mobile radiotelephone itself.
Accordingly, prior art antenna units in general have been designed to have a length C1 of the insulator of whip antenna much longer than a length C3 of the helical antenna. Considering the length C1 of the insulator, a length C2 of the rod antenna section becomes shorter relatively.
However, the prior art antenna units, which are mostly designed to have a length C1 of the insulator much longer than a length C3 of the helical antenna and to have a shorter length C2 of the rod antenna relatively, often give rise to a problem of degraded antenna efficiency for radio signals, since the rod antenna section 14a substantially functions as an operating antenna in an extended position of the whip antenna 14. Furthermore, portable mobile communications terminals are recently being trended toward much smaller size due to striking innovations and improvements in manufacturing technology of hardware components as well as accruing from the users"" ever increasing needs for compactness. Therefore, as the size of a main body of the mobile communications terminal is getting smaller and smaller, its antenna unit is also required to have a shorter length. As a result, such a shorter length of antenna unit may lead to a decrease of communication performance in the mobile communications terminal and also cause its user to be more strongly affected by radiation of probably harmful electromagnetic waves upon using of it.
It is, therefore, an object of the present invention to provide an antenna unit with improved communication performance by increasing its radiation efficiency by means of an elongated rod antenna of a whip antenna in its extended position.
It is another object of the present invention to provide an antenna unit capable of providing a decreased Specific Absorption Rate (SAR), which is referred to as one of the technical criteria for measurement of electromagnetic factors harmful to a human body, proposed in xe2x80x9cIEEE (C95.1)/FCC (P.24) safety specification to radio radiationxe2x80x9d, by means of dispersing the radiation distribution of electromagnetic waves from the antenna unit.
Accordingly, to achieve the above objects of the present invention, an antenna unit for a mobile communications terminal includes an antenna housing extending from a predetermined position on a main body of the mobile communications terminal, the antenna housing having therein an helical antenna; a whip antenna disposed retractably or extendably with respect to the antenna housing, having in its one end an insulator with a length shorter than that of the helical antenna and in its other end a rod antenna; and a conductive tube disposed in a longitudinal direction of the main body under the antenna housing, for receiving the rod antenna in the retracted or extended position of the whip antenna, whereby the insulator is positioned within the helical antenna when the whip antenna is fully retracted into the antenna housing.
Preferably, the conductive tube is made of a metal component. The conductive tube further includes an insulating tube on its inner surface for isolation from the whip antenna. The insulating tube is disposed to extend along said conductive tube, wherein one end of the insulating tube is disposed to protrude in a longitudinal direction from a corresponding one end of the conductive tube, and a diameter of the other end of the insulating tube is made to downwardly decrease within a corresponding other end of the conductive tube. A length of the rod antenna is longer than that of the insulating tube, while a length of the insulator is shorter than that of said helical antenna.